The present invention generally relates to a graft. More particularly, the invention relates to a graft, such as a vascular graft, constructed from two components: a synthetic, biologic or biosynthetic vascular graft component and a reinforcing sleeve component, each of which has an appropriately sized internal diameter so the graft component may be fitted within the sleeve component.
In the medical treatment of patients with diseased arteries or veins, surgeons may replace the failing tissue with prosthetic conduits such as vascular grafts. Conventional grafts, however, can kink or collapse mechanically under a variety of circumstances such as when the graft is bent during the contraction of the surrounding muscle, or when external pressure is applied to the graft during a period of rest taken by the recipient of the graft. One conventional solution to these problems has consisted of the reinforcement of the walls of vascular grafts by the weak attachment of either discrete polymeric rings or continuous spiral polymeric bands to a portion, albeit often a small portion, of the exterior surface of the prosthesis.
Grafts to which such limited reinforcing rings or bands are attached have certain limitations. One limitation of conventionally reinforced vascular grafts is that the reinforcing member may interfere with the creation of an anastomosis. In such a case, the reinforcement must be physically removed by peeling or cutting it off the graft at the time of surgery. Another limitation is that, because the reinforcement is confined to certain areas of the graft, the reinforcement may not necessarily coincide with the area where the reinforcement protection is actually needed. This may happen where the most desirable site to create the proximal and distal anastomosis is in an area of the patient which anatomically presents difficulties to the placement of the reinforced graft. An additional limitation is that the stiffness of the reinforcing member may reduce the circumferential and/or longitudinal compliance of the graft. A non-compliant graft will reduce the pulsatile flow through the graft thereby compromising the ability of the prosthesis to perform naturally. Fourth, the reinforcing members of conventional vascular grafts have a smooth and non-porous surface. Such a surface cannot be penetrated by cellular growth and, accordingly, represents a biologically incompatible interface between the graft and the host tissue. This incompatibility may cause the erosion of the surrounding tissue, the formation of undesirable bursae and fibrotic capsules, or the formation of calcium deposits.
The present invention includes a two-component system, one component of which, the graft component, comprises a synthetic, biologic or biosynthetic graft, including the type detailed in U.S. Pat. No. 4,355,426 to MacGregor and, in part, in U.S. Pat. No. 4,743,252 to Martin and MacGregor and fabricated in the manner detailed in U.S. Pat. No. 4,475,972 to Wong. These patents are incorporated by reference hereinto. The other component, the sleeve component may be formed from synthetic, biologic, or biosynthetic material. The graft component comprises a porous surface and a network of interconnected interstitial pores below the surface, which network is in fluid flow communication with the surface pores.
The second component of the two-component system of the present invention includes a reinforcing sleeve component. Like the graft component, the second component includes a porous surface and a porous subsurface. The sleeve component has an internal diameter that is equal to or larger than the external diameter of the graft component and, as such is sized so that it may be fitted over the first component of the present invention.
The two-component system of the present invention provides advantageously a system which, while providing reinforcement to a graft, overcomes the limitations associated with conventional graft reinforcement systems. For example, by separating the graft component from the reinforcing sleeve component, the blood transporting function handled by the former is isolated from the mechanical load bearing function handled by the latter. This isolation acts to preserve the inherent compliance of the blood transporting member. A non-compliant blood transporting member will interfere with and break up the natural wave flow of in vivo blood, which is a serious disadvantage of prior art reinforced grafts. Generally speaking, prior art reinforced vascular grafts can reduce the pulsatile flow of blood therethrough by a factor of some 10 to 30 percent.
The two-component system of the present invention also allows the separate reinforcing sleeve component to be located at any position along the length of the prosthesis or even across an anastomosis thereby providing support to a localized section of the graft or host artery. For example, during the course of surgery, the slidable reinforcing sleeve according to this invention can be precisely located to provide needed reinforcement at a precise location, such as across a knee joint, a rib cage or the like.
A two-component system, as in the present invention, in which the graft component is reinforced by a sleeve component, also may be fitted into a restricted area without requiring the removal of the segmented reinforcing rings or bands taught in conventional reinforced vascular grafts. Additionally, because the reinforcing sleeve component may be fixed over the graft component through a variety of means, and the means chosen to accomplish the fixation affects to a certain degree the compliance, the resultant compliance of the reinforced graft assembly is adjustable. In addition, compliance is adjustable by winding the fibers of the reinforcing sleeve component at an angle which enhances kink resistance. Compliance is also adjustable by varying the durometer hardness of the fibers from which the reinforcing sleeve component is made.
The structure of the present invention aids in rendering the invention biocompatible and hemocompatible and facilitates its fixation within the body. The former advantage is realized due to the porous surface and subsurface network characterizing the structure of the invention. This structure encourages cellular ingrowth and allows a smooth, thin tissue coating to form and to adhere to the porous surface of the present invention. Desirably, this coating renders the graft resistant to the formation of blood clots which are normally associated with the presence of foreign bodies such as grafts or prostheses, in the blood stream. The latter phenomenon, that is, the fixation of the strengthened graft to the adjacent tissues, is caused also by the formation of the adherent tissue coating on the porous surface. It allows the implant to be incorporated into the cardiovascular system thereby achieving a more secure attachment than previously obtainable.
It is, accordingly, a general object of the present invention to provide an improved graft.
Another object of the present invention is to provide an improved graft assembly having a compliant inner graft component and a reinforcing sleeve component that does not substantially interfere with the compliant properties of the inner graft component.
Additionally, it is an object of this invention to provide an improved reinforced graft whose overall compliance is adjustable.
Another object of this invention is to provide an improved reinforced graft and method of making same.
These and other objects, features and advantages of this invention will be clearly understood through a consideration of the following detailed description.